Microstructure evolvements of a rare-earth filled skutterudite compound during annealing and spark plasma sintering

A dense La0.75Fe3CoSb12 thermoelectric material with uniform grain sizes was synthesized by melt-annealing-Spark plasma sintering (SPS). The evolvements of microstructure of this compound during synthesis were observed. The effects of annealing temperature and time on the grain growth of this compound were studied and the grain growth exponent n and the apparent activation energy Q were estimated to be 2.7 and 381 ± 30 kJ/mol, respectively. It is found that the grain growth of this compound is controlled by the boundary diffusion mechanism at 700 °C. No significant grain growth is observed during sintering by SPS in the sintering temperature range from 540 to 630 °C due to the grains not be ground more fine and a short exposure in high temperature. The grain size after annealing can be kept after sintering by SPS. The results indicate that the final grain size of La0.75Fe3CoSb12 compound synthesized can be modified by controlling the previous annealing temperature under an appropriate sintering temperature and a short dwelling time by SPS.